Gasket for layer-built fuel cells and method for making the same

ABSTRACT

A gasket is provided on a porous sheet in one body. The gasket is thin and has an excellent sealability, and processability when the gasket is built in layer-built fuel cells The gasket is made of liquid rubber and has a hardness not more than 60 (JIS A). Liquid perfluoro rubber and liquid silicone rubber is preferably used for the gasket. And gasket can be made by injection molding.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a gasket for layer-built fuelcells. More precisely, the present invention relates to a gasket, for asheet component of the layer-built fuel cells, having an excellentsealability when used in the layer-built fuel cells. Moreover thepresent invention relates to a gasket having an excellent processabilitywhen the layer-built fuel cells is assembled.

[0003] Still more, the present invention relates to a method for makinga gasket, for a sheet component of the layer-built fuel cells, having anexcellent sealability when used in the layer-built fuel cells.

[0004] 2. Description of the Related Art

[0005] Fuel cells, electrochemical device for continuously convertingchemicals—a fuel (hydrogen) and an oxydant (oxygen)—into direct currentelectricity, have electronic-conductor electrodes on whichelectrochemical reactions are taking place. The electrodes—a fuelelectrode and an oxygen electrode—are usually coated with a fine powderof platinum-based catalysts thereon. Generation of electricity iscarried out through electrochemical reactions which differ from aconventional oxidation reactions.

[0006] As for electrodes of the fuel cells, materials having a highelectronic conductivity, an excellent stability for electrochemicalreactions and an excellent anti-degradation property for electrolytessuch as phosphoric acid or the like, have been used so far. For example,an amorphous carbon, or a powder or a fiber made of graphite, has beenused conventionally. Especially, electrodes made of carbon easily acceptelectrons from hydrogen, a fuel, when hydrogen is ionized duringelectrode reactions. The electron accepted by electrodes becomeselectric current and electric voltage. Carbon electrodes have also highelectric conductivity and facilitate inonization of hydrogen in theelectrode reaction.

[0007] Since reactions on the electrodes are carried out by contactprocesses between gas (a fuel) and a solid (electrode), the surface ofthe electrodes is required to be as large as possible for securing thespeed of the reaction. This means that the electrodes should have porousstructure in its surface portion to secure large contact surface areabetween gas and the electrodes. Carbon having excellent electronconductivity is generally stiff and brittle so that the physicalstrength of the carbon plate having porous structure (porosity is in therange of from about 40% to about 70%) tends to become low. These carbonplates are used in fuel cells as a current-collecting electrode(separator), a reaction electrode or the like. Fuel cells are built upusing these sheet-like components such as the current-collectingelectrode, the reaction electrode and an ion-exchange membrane.

[0008] Moreover, fuel cells are required to be sealed so as not to leakfuel gas (hydrogen, oxygen or the like) and liquid (liquid electrolyteor water produced in the electrochemical reaction) from the fuel cellsin order to secure efficiency of power generation, longevity andstability of the device or the like. Especially, these fuel gasses orliquids tend to leak or permeate out of the fuel cells at the peripheryof the carbon plates or the ion-exchange membranes.

[0009] In order to prevent liquid or gas from leaking, various sealssuch as gaskets (Japanese unexamined patent 9-231987, 7-263004, 7-226220and 7-153480), rubber plates with cellular rubber layer thereon whichare used as gaskets (Japanese unexamined patent 7-312223), haveconventionally been used.

[0010] As is shown in FIG. 13 which is one of prior arts, there areseveral components such as a current-collecting electrode (separator) 2,an ion-exchange membranes 3 interposed between a membrane-fixed reactionelectrode 4, a gasket or the like. The gasket is made of a cellularrubber 6 and a rubber plate. But these prior arts did not aim at seekingseals having thin-wall, good processability in building up fuel cells, aproperty hard to displace from its initial sealing place, goodsealability even at low sealing pressure, uniformity of sealing pressurearound its circumference or the like. That is, conventional gaskets,which are not unitized with sheet-like components, can notsatisfactorily provide seals with thin-wall, good processability inbuilding up the fuel cells, a property hard to displace from its initialsealing place or the like.

[0011] What is more, fuel cells have usually hundreds of carbonelectrodes and sheets (separators and ion-exchange membranes) having athickness of from about 0.1 mm to a few mm and one side dimension offrom about 10 cm to about 50 cm in square or rectangular shape. Eachsheet is so thin that it tends to get wrinkled. And carbon sheets haveundulation in itself. From these causes, leaks of gas or liquid from thefuel cells have often been observed at the conventional sealing portionsdue to displacement or uneven pressure in sheets or electrodes. Therehave also been a big problem concerning processability in stacking eachsheet to its correct position.

[0012] Materials made of polytetrafluoroethylene resin (PTFE resin) havebeen generally used as a seal for a phosphoric acid type fuel cellswhich is now regarded as a most promising one. Polytetrafluoroethyleneresin can be used as a sealing material under such a severe condition asthe presence of concentrated phosphoric acid at about 200° C. in thephosphoric acid type fuel cells. Seals made of polytetrafluoroethyleneresin are, however, hard in hardness so that sealing pressure must behigher to get a good sealing condition. But high sealing pressure causesbreakdown of the carbon electrodes because the carbon electrodes arebrittle due to its porosity mentioned above. And seals made ofpolytetrafluoroethylene resin have also such a shortcoming as difficultyin processing to make the seal. Ion-exchange membranes are also brittlewhen dried, so that strong stress added on the membranes may causedamage of the membranes.

[0013] Seals made of polytetrafluoroethylene have an excellentresistance against heat and chemicals in practical use as mentionedabove, but can not completely seal the surface of the porous carbonplate because there is a convexo-concave portion on the surface of theelectrode. Therefore seals made of polytetrafluoroethylene resin havebeen used with accepting a certain amount of leaking of fuel gasses, orused on carbon electrodes which are burnt after flattened and smoothedby coating on the surface of the carbon electrodes withpolytetrafluoroethylene aqueous dispersion or the like, and then sealsare pressed onto the polytetrafluoroethylene-coated carbon electrodes(Japan Unexamined Patent 58-078372, 59-068171). Therefore there havebeen some troubles such as time-consuming in process of manufacturingseals, instability in sealing property and difficulty in makingthin-walled sealing members.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to provide a gasket, whichis used for layer-built fuel cells, the gasket being low in height toallow the layer-built fuel cells to be more compact in size and showingan excellent sealing property even at a low sealing pressure. Anotherobject of the invention is to provide a gasket, which has an excellentprocessability when the layer-built fuel cells are assembled.

[0015] Still another object of the present invention is to provide amethod for manufacturing a gasket having no weld portion in itself,having an excellent sealability, and being used for a layer-built fuelcell.

[0016] The object of the present invention can be achieved by a gasketwhich is formed on a sheet component of fuel cells, and made of a liquidrubber vulcanizates having a hardness preferably not more than 60 (JIS Aof JIS K 6301), the vulcanizates being unitized with the sheet.

[0017] Liquid rubbers used in the invention have a viscosity not morethan 10⁴ Pa·s (at 25° C.). Liquid perfluoro rubber is preferably used inthis invention because perfluoro rubber has an excellent heat resistanceand chemical resistance. Moreover a polytetrafluoroethylene fine powdercan preferably be added into the liquid perfluoro-rubber for decreasinggas permeability. When porous carbon plates made of fibrous carbon areused as the sheets, liquid rubbers are infiltrated into the porouscarbon plates, thereby the infiltrated portions become non-permeateportions against gas or aqueous electrolyte or water produced viaelectrochemical reactions, and become gasket portions too.

[0018] When porous carbon plates made of carbon other than the fibrouscarbon are used as the sheets, the sealing portion (gasket) is made,integrally with the porous carbon plates, on the surface of the porouscarbon plate or on a groove which is formed on a surface of the porouscarbon plate.

[0019] When ion-exchange membranes are used as the sheets, the sealingportion is made, integrally with the ion-exchange membrane.

[0020] The sealing portions of these cases have preferably a hardness(JIS A) not more than 60 and are made of various liquid rubber having aviscosity not more than 10⁴ Pa·s (at 25° C.).

[0021] Another object of the present invention can be achieved by aprocess of an injection-molding of liquid rubbers under vacuumcircumstances. The molding processes of the present invention is asfollows, first sucking out air in a closed space between an upper andlower mold, then closing the molds and injecting liquid rubber on apredetermined place of the surface of the porous sheet, and then curingthe rubber in a predetermined period of time. There is no weld portionbecause no air is substantially in a cavity of the mold.

[0022] These features and advantages of the inventions will becomeapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a diagram of injection molding system;

[0024]FIG. 2 is a cross sectional view of the mold of the injectionmolding;

[0025]FIG. 3 is a diagram showing a flowchart of manufacturing processfor making gaskets;

[0026]FIG. 4 is a cross sectional view of the mold of the secondembodiment;

[0027]FIG. 5 is a cross sectional partial view of a sheet that has ahole connected both side of the sheet to secure the gasket in the sheet;

[0028]FIG. 6 is a cross sectional partial view of a porous sheet thathas a gasket in the hole in FIG. 5;

[0029]FIG. 7 is a cross sectional partial view of a gasket A provided ona sheet;

[0030]FIG. 8 is a cross sectional partial view of a gasket B provided ona sheet;

[0031]FIG. 9 is a cross sectional partial view of a gasket C provided ona sheet;

[0032]FIG. 10 is a cross sectional partial view of a gasket D providedon a sheet;

[0033]FIG. 11 is a plane view of a sheet with a groove placed on thesurface of the sheet at a peripheral portion.

[0034]FIG. 12 is a cross-sectional view taken along the line X-X of FIG.11.

[0035]FIG. 13 is a cross sectional view of each component which is usedin the conventional layer built fuel cells.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] As to a plane sheet, any type of porous carbon plate andion-exchange membrane can be used in the present invention as anelectrode or a separator for fuel cells. Any type of porous carbon platecan be used. Generally, porous carbon plate can be classified into twotypical kind of plates. One is a carbon plate made of carbon powderwhich is bound using resin such as phenol resin or the like and then theplate is burnt to make final porous carbon plate. This type of porouscarbon plate has a closed cell (or unicellular foam). So liquid rubbershaving even relatively low viscosity can not easily enter into theinside of the porous carbon plate. Even gas can not penetrate throughthe carbon plate.

[0037] Another type of porous carbon plate is made of carbon fiber whichis immersed in a liquid such as an aqueous dispersion ofpolytetrafluoroethylene resin, and then the immersed carbon fiber isdried and press-molded to make final porous cabon plate. This type ofporous carbon plate has relatively high porosity when compared withformer one. So liquid rubbers having relatively low viscosity can enterand relatively easily penetrate into the inside of the carbon plate.Polytetrafluoroethylene resin acts as a repellent of water produced inelectrochemical reaction or liquid electrolytes, to prevent theelectrode from wetting.

[0038] As to the ion-exchange membranes, any type of membranes can beused, but membranes made of fluoropolymer is generally used for fuelcells.

[0039] As to a liquid rubber which can be used in the present invention,various kind of liquid rubber can be used such as a liquid siliconerubber, a liquid perfluoro rubber, a liquid nitrile rubber, a liquidethylene-propylene-diene rubber, a liquid fluoro-rubber or the like.However a liquid perfluoro rubber and a liquid silicone rubber can bepreferably used in the present invention. These liquid rubbers have arelatively low viscosity and can easily be injection-molded. Theseliquid rubbers can flow easily in a mold so that molding pressure atmolding is relatively low enough to prevent the carbon plate, which isplaced in the mold, from collapse by a molding pressure. Other moldingmethods such as compression molding or transfer molding can also beused.

[0040] As to the hardness of the vulcanizate of the liquid rubber,preferably hardness (JIS A) not more than about 60, more preferablywithin the range of about 40 to about 5, is selected. This is becausesealing performance of these vulcanizates can be achieved even atrelatively low contact sealing pressure. However, liquidperfluoro-rubber, which contains polytetrafluoroethylene fine powder,and having a hardness more than about 60 can be used when an excellentanti-gas permeability is required.

[0041] The vulcanizates having a hardness not more than 60 can be madeof a liquid rubber such as a liquid silicone rubber having a viscosityof not more than about 500 Pa·s, preferably within a viscosity of fromabout 300 to about 30 Pa·s (at 25° C.), a liquid perfluoro rubber havinga viscosity of not more than 10,000 Pa·s, preferably not more than 1000Pa·s (at 25° C.), a liquid nitrile rubber, a liquidethylene-propylene-diene rubber, a liquid fluororubber or the like.Liquid silicone rubbers and liquid perfluoro rubbers can preferably beused in the present invention. Liquid rubbers having these range ofviscosity can easily enter or interpenetrate into porous carbon plateand has an excellent formability or moldability due to its lowviscosity. Polytetrafluorotehylene fine powder can be added into liquidperfluoro rubber as a repellant of aqueous electrolytes or waterproduced during electrochemical reactions and as a filler whichdecreases permeability coefficient.

[0042] As to the polytetrafluoroethylene fine powder, average particlediameter within the range of from about 20 μm to about 40 μm canpreferably be used.

[0043] These liquid rubbers are commercially available. For instance,liquid silicone rubber are supplied under the name of KE1950-20(A.B) orKE1950-10(A.B) (heat curable two-type liquid rubber) by ShinetsuChemicals Co. As for liquid perfluoro rubber, X-70-709 and SIFEL 3500(A.B) (heat curable two-type liquid rubber) are supplied by the samecompany. In the case of two-part liquid type perfluoro rubber such asSIFEL 3500, rubber component having the viscosity not more than 10⁴ Pa·sis preferably used.

[0044] X-70-709 and SIFEL 3500 (A.B) has a following basic chemicalstructure I (perfluoro ether) in its main chain.

[0045] KE1950-20(A.B) and KE1950-10(A.B) have a following basic chemicalstructure II in their main chain.

[0046] These liquid rubbers can be vulcanized by injection molding orthe like. These liquid rubbers are, for example, injected into thegroove formed on the surface of the sheet (plate), using a mold having agroove corresponding to the protrusion of the gasket. Injection moldingcan be carried out at a relatively low injection pressure of about 2 to20 MPa.

[0047] Molding can be, for example, carried out as follows.

[0048] As is shown in FIGS. 11 and 12, on a surface of the plane porouscarbon plate, for example, a groove 65 is provided along an inner partof an outer periphery 70 of the plate 61. The depth D2 of the groove 65is within the range of about 0.05 mm to about 3 mm, preferably withinthe range of about 0.1 mm to about 1 mm. The width W2 of the groove 65is within the range of about 1 mm to about 10 mm, preferably within therange of about 2 mm to about 5 mm. On or in the groove 65, gasket 63having a convex shape (protrusion or lip) is formed as is shown in FIGS.7 to 10. The shape of the protrusion 62 can be various shapes such asmountainous, inclined mountainous, mountainous with bifurcated peaks orthe like. The width W1 of the protrusion in the vicinity of the footthereof can be determined discretionary, however preferably within therange of about 0.2 mm to about 10 mm, more preferably about 1 mm toabout 5 mm. The height h1 of the protrusion from the foot to the peakthereof can also be determined discretionary, however preferably withinthe range of about 0.1 mm to about 3 mm, more preferably about 0.2 mm toabout 2 mm.

[0049] The gasket of the present invention has a base portion 64 tightlysecured in the groove 65. The groove 65 is formed for preventing thegasket 63 from displacement from its initial position.

[0050] When the porous carbon plate made of carbon fiber is used as thesheet, the liquid rubber easily penetrate into the porous plate becausethe viscosity of the liquid rubber is low enough to enter into theplate. The gasket in this case is tightly secured in and on a portionwhere the liquid rubber is placed.

[0051] The gasket of the present invention can be made, for example, bythe following steps using an injection molding machine, first closingmolds (upper mold and lower mold) relatively loosely and then placingthe nozzle of the injection machine on an inlet of the mold so as tomake a closed space between these two molds, next sucking out air fromthe closed place between the upper and lower molds, then closing themolds, and then injecting liquid rubber into the mold.

[0052] Degree of vacuum in the closed space is set not more than 30Torr, preferably not more than 20 Torr, more preferably not more than 10Torr. Degree of vacuum is more than the value mentioned above, the weldline(s) tend to appear on gaskets produced, and bonding strength betweenthe gasket and the sheet which has a void on the surface tends to bepoor.

[0053] The gasket of the present invention can also be made in one bodyon both side of the porous sheet simultaneously by injection molding ofliquid rubber on the sheet which have a plurality of hole in the sheet,the hole being connected between both plane surface of the sheet.

[0054] The injection machine has at least two molds (upper mold andlower mold). The two molds are placed face to face with an interspacenot more than about 2 mm. Inner space between the two molds is closed byan O-ring or the like (step S 101, as shown in FIG. 3). Then the nozzleof the injection machine touches onto the inlet, through which liquidrubber enter into the mold, to shut off the space in the mold from outerenvironment (S 102, in FIG. 3). Then air in the closed space is vacuumedout through a passage made on a parting surface of the mold. A shut offvalve is formed in the nozzle of the injection machine to prevent theliquid rubber from getting sucked into the mold through the inlet by anegative pressure (S 104, in FIG. 3). The molds are then completelyclosed after the pressure in the closed space becomes to a predeterminedpressure (S 104, in FIG. 3). Liquid rubber is then injection-molded intothe vacuumed space to mold a gasket.

[0055] The sheet is protected against damage because molding can becarried out at relatively low pressure, because liquid rubber have a lowviscosity.

[0056] A porous sheet with two gaskets having each mountaineous or lipportions on both surfaces of the porous sheet can simultaneously beprovided by injection molding a liquid rubber on one surface of theporous sheet. When the sheet is thin in thickness, and there is a needto form a gasket on both surface of the sheet, it is often difficult toform a gasket on one surface without damage of the sheet. This isbecause the sheet tends to be damaged if there is no support on theother side of the groove. It is possible to make a support portion in amold to support the bottom of the other groove, but the cost to make aspecial mold tends to increase. And the structure of the mold becomescomplex so that stable molding can not often be secured because theheight of the gasket tend to fluctuate by a tolerance of the depth ofthe groove or a tolerance in mold manufacturing.

[0057] To avoid these problems, holes penetrating through the sheet inthe direction of its thickness are provided in the groove of the sheet.When liquid rubber is injected onto one of the groove of the surface ofthe sheet, liquid rubber also simultaneously runs through the holes intothe other side of the groove to make another gasket. These gaskets aretightly secured on the sheet because these gaskets 7 and 8 engage withthe holes 40 c as shown in FIG. 6.

[0058] In the meantime when the porous carbon plate made of carbon fiberis used, liquid rubbers can be placed on a desired position of thesurface of the carbon plate and then pressed by a mold and then heatedit into vulcanizates.

[0059] The thus obtained porous carbon plates having a vulcanizedsealing portion made of liquid rubber in the groove or on the surface ofthe porous carbon plate are used in fuel cells together with othercomponents such as current-collecting electrodes, ion exchange membranesand reaction electrodes. The sealing portion can effectively seal aportion between each electrode or sheet.

Effect of the Invention

[0060] The gasket of the present invention is formed on the surface ofthe sheet in one body. So there is no need to place an additional sealor gasket on the sheet when the fuel cells is assembled. It is possibleto place the gasket accurately in a predetermined position because thegasket of the invention is bonded tightly and held on a predeterminedposition of the sheet. There is no displacement or twist of the gasketof the invention. So it is possible to make the gasket thinner andslender.

[0061] Moreover hardness (JIS A) of the gasket of the present inventionis preferably lower than about 60, so that sealing ability can beachieved even at relatively low sealing pressure (about 0.5 MPa). Thislead to that the carbon plate is not damaged by the sealing pressure.

[0062] The liquid perfluoro rubber has an excellent chemical resistanceand an excellent heat resistance so that the gasket made of liquidperfluoro rubber of the invention has an excellent resistance for use ina phosphoric acid-type fuel cell in which concentrated phosphoric acidis used at about 200° C.

[0063] The gas permeability of the liquid perfluoro rubber can beimproved considerably with the amount of polytetrafluoroethylene finepowder in its composition. The fuel cell is required to decrease fuel(gas) leaking from fuel cells device, so these type of compositionhaving an excellent anti-gas permeability are desirable for use in fuelcells.

[0064] In addition, there is no need to use an adhesive, because theporous carbon plate has a void in itself. These void acts like a anchorto secure relatively strong bonding with the liquid rubber vulcanizate.The liquid rubber can enter into these voids because the liquid rubberhas relatively low in viscosity. Absence of adhesives is desirable forfuel cells because adhesives may contaminate fuel cells to decrease theefficiency of power generation. However adhesives may be used ifadhesives do not exert a crucial damage on fuel cells.

[0065] When there is no void on the surface of the carbon plate as isthe case of the porous carbon plate made of carbon powder, voids thatexist inside of the porous carbon plate appear on the surface by cuttingthe surface.

[0066] When liquid rubber is used in the porous carbon plate made ofcarbon fiber, the liquid rubber penetrates into the porous carbon plateand fill up the void. The portion where liquid rubber fill up becomesnon-air-permeate portion which can prevent gas or liquid from leakingthrough the portion. And this portion also becomes a gasket portion.

[0067] Examples of the sheets in the invention are component parts oflayer-built fuel cells such as plate-like porous electrodes, polymericsolid electrolytic membranes (ion-exchange membranes), separators,cooling plates, modules, manifolds or the like. Porous electrodes madeof carbon are preferably used as the member to be sealed in theinvention. Sealing can be secured under a contact pressure less than thebuckling strength of the electrode when pressure is applied in thedirection of the thickness of the porous carbon plate.

[0068] More specifically, sealing materials (or gaskets) are made ofelastic materials so that sealing materials can sealingly face-contactwith another plate at a relatively low contact pressure even if there issomewhat undulation on the surface of the gasket.

[0069] Curing or vulcanizing of the sealing materials is carried outafter the materials infiltrate into the void, so that bonding oradhesion between the sealing materials and the member to be sealed, canbe physically and completely achieved.

[0070] Conventional sealing has been carried out by applying relativelygreater contact pressure on a gasket. But in the present invention thereis almost no compression buckling of the electrodes when compared withthe conventional sealing methods. In addition to these advantagesmentioned above, there is another advantage in processability inmanufacturing fuel cells.

[0071] According to the process of the present invention, weldingportion through which gas leakage ma occur, can be eliminated from thegasket because the molding is carried out under vacuum condition.

[0072] Vacuum condition is maintained because injection nozzle has ashut off valve, thereby even liquid rubber having a low viscosity cannot inadvertently enter into the mold. Injection molding is carried outunder vacuum condition so that welding portion in the gasket caneffectively be eliminated, and also strong adhesion between the sheetand gasket can be achieved because liquid rubber having a low viscositycan easily enter even into small convex-concave voids existing on thesheet surface. Welding portion tends to cause gas leakage.

[0073] When thin porous sheet is used to make two gaskets on both sideof the sheet, two gaskets on both side of the sheet can simultaneouslybe made by providing a hole or holes which is or are formed in the thinporous sheet. The liquid rubber can flow onto predetermined places onboth surfaces of the sheet through the hole or holes.

[0074] Still more, the sealing materials in the present invention can beused for various seals such as for separators in fuel cells, moduleswhich combine several fuel cells in one body, cooling plates whichremove generated heat during power generation or the like.

[0075] Embodiment

[0076] The present invention will be explained by referring embodiments.

[0077] Reference Embodiment Liquid perfluoro-rubber: SIFEL 3500 (A · B)manufactured by Shinetsu Chemicals Co. Tow-type liquid perfluoro-rubber(thermosetting type) Liquid A:about 120 Pa · s (curing component) LiquidB: about 700 Pa · s poise (rubber component) Polytetrafluoroethylene:Molding powder M-12 manufactured by fine powder Daikin Co. (averagediameter: 25/μm)

[0078] Into the Liquid A, a predetermined weight ofpolytetrafluoroethylene fine powder (0, 10, 20, 30 or 50% by weightbased on the total amount of a composition) was added and then blendedby kneader. Then the equal amount of the Liquid B which is equal amountof the Liquid A, was added into the blended compounds to produce thecompositions which contain various amount of polytetrafluoroethylenefine powder.

[0079] Physical properties of vulcanizates were then measured asfollows.

[0080] Contact Angle

[0081] The compositions were press-cured for 30 minutes at thetemperature of 150° C., to obtain sheets having thickness of 1 mm.Contact angles of the sheets were measured using a contact angle meter(produced by Kyowa Surface Chemical Co.). Contact angle is a value toestimate the degree of repulsion of water. The rate of theelectrochemical reactions of fuel hydrogen gas increases with increasingthe degree of water repulsion. The rate of leakage of aqueouselectrolytes via gaskets or through a gap between each gasket will alsoincrease with decreasing the degree of water repulsion.

[0082] Permeability Coefficient of Gas

[0083] The compositions were press-cured for 30 minutes at thetemperature of 150° C., to obtain sheets having thickness of 1 mm.Permeability coefficients of nitrogen (N₂) of the sheets were measuredat 25° C. using a gas permeability tester. The unit of the permeabilitycoefficient of nitrogen gas is shown in cm³/cm²·sec·Pa.

[0084] Hardness (JIS A)

[0085] The compositions were press-cured for 30 minutes at thetemperature of 150° C., to obtain sheets having thickness of 1 mm. Thehardness of vulcanizates were measured based on JIS K-6253.

[0086] Test results are shown in next Table. TABLE Gas PTFE fine powderContact permeability Compound added (% by angle coefficient Hard- Noweight) (degree) (cm³/cm² · sec · Pa) ness 1  0 40 0.96 × 10⁻¹³ 50 2 1065 0.20 × 10⁻¹³ 55 3 20 80 0.07 × 10⁻¹³ 63 4 30 90 0.05 × 10⁻¹³ 78 5 4095 0.05 × 10⁻¹³ 90

[0087] Embodiment 1

[0088] Ten (10) percent by weight of an aqueous dispersion ofpolytetrafluoroethylene (Teflon 30-J by Mitsui Dupont FluorochemicalCo.) based on the total amount of both aqueous dispersion and a choppedcarbon fiber (M 201 by Kureha Chemical Co.: average length of fiber 130μm, average diameter of fiber 12.5 μm ) was infiltrated into the choppedcarbon fiber, the infiltrated carbon fiber was dried at 50° C. Then itwas press-molded at 400° C., thereby obtaining a porous carbon sheet(degree of porosity, 55%) having a thickness of 0.5 mm.

[0089] The porous carbon sheet was placed at a bottom of an inner hollowcylinder, and then the mixture of the equal amount of the compound 1 (asshown in Table, Liquid A and Liquid B (SIFEL 3500(A.B))) was coated onthe porous carbon sheet in a circle, around the outer periphery of theporous carbon sheet. Then the porous sheet was pressed into the totalthickness of 0.8 mm using another cylinder which had a flat end surface.Then curing was carried out in an oven for 30 minutes at 150° C.

[0090] The total thickness of the products was 0.75 mm when measuredafter curing. Fracture was observed in the inside of the porous carbonsheet when bonding strength (JIA K 6256) of the product was tested.There was no fracture in the interface between the rubber portion andthe porous carbon portion, thereby it can be concluded that the bondingstrength between the rubber and the porous carbon sheet is excellent.Furthermore, when gasket-like seal portion of the products were cut andobserved under a microscope, it was confirmed that vulcanizates of theliquid perfluoro-rubber interpenetrated into and fill up almostcompletely the porous portion of the porous carbon sheet. The thicknessof the rubber portion of the gasket-like seal portion was 0.25 mm, asagainst the aimed thickness of 0.3 mm.

[0091] Embodiment 2

[0092] In the embodiment 1, compound No.3 was used instead of compoundNo.1. The total thickness of the sealing portion of the product was 0.83mm. Fracture was observed in the inside of the porous carbon sheet. Thisphenomenon shows the bonding strength is excellent.

[0093] Embodiment 3

[0094] In Embodiment 1, compound No.5 was used instead of compound No 1.The total thickness of the sealing portion of the product was 0.85 mm.Fracture was observed in the inside of the porous carbon sheet whenbonding test was carried out. This phenomenon shows bonding strength isexcellent.

[0095] Embodiment 4

[0096] Twenty (20) percent by weight of solvent naphtha based on theweight of the polytetrafluoroethylene powder (Polyflone, by Daikin Co. )was added to the polytetrafluoroethylene powder, and then the thusobtained paste-like mixture was extruded at 150° C. The extruded sheetwas stretched to 200% at a room temperature and then the 200% stretchedsheet was baked for 10 minutes at 340° C., to obtain a stretched poroussheet (0.35 mm in thickness and 62% of porosity) made ofpolytetrafluoroethylene. The thus obtained stretched porous sheets havean excellent flexibility. The porous portion of the sheets wasrelatively easily collapsed by pressure, to be a sealant having anexcellent sealability.

[0097] Twenty (20) percent by weight of the mixture consisting of LiquidA and Liquid B of the liquid perfluoro-rubber (SIFEL 3500) based on theweight of the stretched porous sheet was infiltrated into the stretchedporous sheet. And then the porous carbon sheet having thickness of 0.5mm which was obtained in Embodiment 1 was placed on the stretched poroussheet. Vulcanization was carried out, by setting the thickness of thevulcanizates to 0.7 mm, for 30 minutes at 150° C., as is shown inEmbodiment 1.

[0098] Similar adhesive failure tests as shown in Embodiment 2 werecarried out on the vulcanizates. Fracture was observed in the inside ofthe porous carbon sheets. According to the results of the test,excellent adhesioness was confirmed.

[0099] Embodiment 5

[0100] The surface of a resin-immersed type carbon plate (IKC-33 by Toyocarbon Co. thickness of the plate: 2 mm) was cut to make a groove (widthW2: 3.0 mm, depth D2: 0.3 mm) 65 on the surface around an outerperiphery of the plate (as shown in FIG. 7 ˜10 and 11). Injectionmolding was carried out in such a way similar to Embodiment 10 whichwill be described later. Liquid silicone rubber was injection moldedinto the groove at the pressure of 19.6 MPa using molds havingpredetermined shapes, to obtain various carbon plate with a gasket (A˜D)made of silicone rubber and combined with the plate in one body.

[0101] Carbon plate with gasket A:

[0102] Gasket A is a standard type in shape, the lip or mountainousportion 62 of the gasket 63 is approximately symmetrical with respect toa vertical line as shown in FIG. 7. The gasket A is compressedapproximately downward when used. The root portion 64 of the gasket 63is embedded in the groove 65 of the carbon plate 61. Dimensions of thelip are as follows, h1: 2 mm, W1: 2 mm. Small circles 68 are void in theporous carbon sheet.

[0103] Carbon plate with gasket B:

[0104] Gasket B has a lip somewhat slanting toward outward or inwarddirection relative to the plate as shown in FIG. 8. The lip ormountainous portion 62 slants somewhat right-hand side as shown in FIG.8. Other reference numerals are same as in FIG. 7. Slanting angle θ is70°. Other dimensions of the lip are the same as the carbon plate withgasket A.

[0105] Carbon plate with gasket C:

[0106] Gasket C has two small lips 67 placed in parallel manner in thetop of the mountain 66 as shown in FIG. 9. The two small lips 67 areapproximately symmetrical with respect to a vertical line. This type ofgasket can seal with relatively low sealing pressure. Other referencenumerals are same as in FIG. 7. Dimensions of the lip are as follows,h1: 2 mm, h2: 0.7 mm.

[0107] Carbon plate with gasket D:

[0108] Gasket D has two small lips 77 placed in parallel manner in thetop of the mountain 66 as shown in FIG. 10. The two small lips 77 slantsoutward direction relative to the mountain 66 in FIG. 10. Slanting angleθ of the small lip is 70°. Other dimensions are the same as the carbonplate with gasket C.

[0109] Liquid silicone rubber (KE1950-20(A.B) by Shinetsu Chemicals Co.)used in this embodiment is translucent, has a viscosity of about 150Pa·s (at 25° C.), and gives hardness (JIS A) of 20 after the liquidsilicone rubber is vulcanized. Injection molding was carried out in amold at 150° C. for 60 seconds.

[0110] Embodiment 6

[0111] In Embodiment 5, instead of the liquid silicone rubber(KE1950-20(A.B)), another liquid silicone rubber (KE1950-10(A. B) byShinetsu Chemicals Co.) which is translucent, has a viscosity of about60 Pa·s (at 25° C.) and gives hardness (JIS A) of 13 after the liquidsilicone rubber is vulcanized, was used.

[0112] Embodiment 7

[0113] In Embodiment 5, instead of the liquid silicone rubber(KE1950-20(A.B)), another liquid silicone rubber (X-70-709, by ShinetsuChemicals Co.) which is translucent, has a viscosity of about 30 Pa·s(at 25° C.) and gives hardness (JIS A) of 35 after the liquid siliconerubber is vulcanized, was used.

[0114] Embodiment 8

[0115] In Embodiment 5, instead of the liquid silicone rubber(KE1950-20(A.B)), liquid perfluoro rubber (SIFEL 3500 (A.B)), byShinetsu Chemicals Co.) which has a viscosity of about 400 Pa·s (at 25°C.) and gives hardness (JIS A) of 50 after the liquid perfluoro rubberis vulcanized, was used.

[0116] Embodiment 9

[0117] In Embodiment 5, instead of the liquid silicone rubber(KE1950-20(A.B)), liquid perfluoro rubber (SIFEL 3500 (A. B), byShinetsu Chemicals Co.) which has 10% by weight ofpolytetrafluoroethylene fine powder and gives hardness (JIS A) of 55after the liquid perfluoro rubber is vulcanized, was used. the viscosityat 25° C. of this compound was about 500 Pa·s.

COMPARATIVE EXAMPLE 1

[0118] In Embodiment 5, instead of the liquid silicone rubber(KE1950-20(A.B)), another liquid silicone rubber (KE1950-70 (A.B), byShinetsu Chemicals Co.) which is translucent, has a viscosity of 750Pa·s (at 25° C.) and gives hardness (JIA A) of 68 after the liquidsilicone rubber is vulcanized, was used.

[0119] Properties other than hardness (JIS A) of the vulcanized liquidrubbers are shown in Table 1. These rubber were press-molded at 150° C.for 10 minutes and then post cured at 200° C. for 4 hours. TABLE 1Vulcan- izate of Liquid silicone SIFEL rubber KE1950-20 KE1950-10X-70-706 KE1950-70 3500 Tensile 6.4 3.9 5.9 7.8 7.3 strength (MPa)Tearing 30 13 10 49 11 strength (KN/m) Elonga- 900 700 400 350 300 tion(%) Specific 1.10 1.08 1.88 1.15 1.89 gravity (−)

[0120] The thus obtained carbon plate having gasket A˜D were tested. Theresults of the test are shown in Table 2. Sealability A gasket formed ona groove of a porous carbon plate was pressed to another plane carbonplate at 25% rubber compression ratio. Then leaking test using heliumgas was carried out under the pressure of 0.2 MPa. ∘:no leaking,Δ:unstable in sealing, x:leaking Sealing pressure A gasket formed on agroove of a porous carbon plate was pressed to another plane carbonplate at 40% rubber compression ratio. Sealing pressure was calculatedfrom the stress of gasket. ∘:less than 2N/mm of length of the gasket,Δ:2˜5N/mm, x:more than 5N/mm Contactability A plane transparent glassplate was between gasket and a pressed to a gasket formed on a groove ofmember to be sealed plane carbon plate at 25% to 40% rubber compressionratio. Visual observation of the contact condition was made through theglass plate. ∘:good, Δ:a little uneven, x:uneven

[0121] TABLE 2 Em. Em. Em. Em. Em. Comparative 5 6 7 8 9 example 1Carbon plate with gasket A Sealability ◯ ◯ ◯ ◯ ◯ ◯ Sealing ◯ ◯ ◯ ◯ ◯ Δpressure Contactability ◯ Δ ◯ ◯ ◯ ◯ between gasket and a member to besealed Carbon plate with gasket B Sealability ◯ ◯ ◯ ◯ ◯ ◯ Sealing ◯ ◯ ◯◯ ◯ Δ pressure Contactability ◯ ◯ ◯ ◯ ◯ ◯ between gasket and a member tobe sealed Carbon plate with gasket C Sealability ◯ ◯ ◯ ◯ ◯ ◯ Sealing ◯ ◯◯ ◯ ◯ Δ pressure Contactability ◯ ◯ ◯ ◯ ◯ ◯ between gasket and a memberto be sealed Carbon plate with gasket D Sealability ◯ ◯ ◯ ◯ ◯ ◯ Sealing◯ ◯ ◯ ◯ ◯ Δ pressure Contactability ◯ ◯ ◯ ◯ ◯ ◯ between gasket and amember to be sealed

COMPARATIVE EXAMPLE 2

[0122] A gasket having a round shape in cross section and made ofclay-like black colored fluoro rubber (mixture of fluoro rubber E60C byDupont, MT carbon black, Ca(OH)² and MgO) was placed on a carbon plate,and then similar tests were carried out. The test results showed a goodsealability (∘), a poor sealing pressure (X) and a little uneven incontactability (Δ).

COMPARATIVE EXAMPLE 3

[0123] A gasket having a round shape in cross section and made ofclay-like black colored cellular nitrile rubber was placed on a carbonplates, and then similar tests were carried out. The test results showeda rather poor sealability (Δ), a rather poor sealing pressure (Δ) and alittle uneven in contactability (Δ).

[0124] Properties of the fluoro rubber and the cellular nitrile rubberused in Comparative Example 2 and 3 are shown in Table 3. TABLE 3Cellular nitrile Fluoro rubber rubber Hardness (JIS A) 70 35 Tensilestrength 14.5 1.4 (Mpa) Tearing strength 26 — (KN/m) Elongation 230 160(%) Specific gravity 1.85 0.82 (−)

[0125] Embodiment 10

[0126] In FIG. 1, a liquid injection molding machine 11 which can beeffectively used in the present invention. A plunger 15 transportsliquid rubber, colorant and curing agent from liquid rubber tank 12,colorant tank 13 and curing agent tank 14 to the injection machine 16.These materials are injected from the machine 16 into the mold 17, tomanufacture a gasket. The injection machine 16 has an oil motor 18, ascrew 20 driven by an injection cylinder 19 and an injection tube 21. Ina nozzle 22 in the tip portion of the injection tube 21, there is ashut-off valve 23 that opens and shuts to control flow of liquid rubbercomposition into the mold 17. A vacuum pump 24 is connected to the mold17.

[0127]FIG. 2 shows the detail of the mold 17. An upper platen 25, athermal insulating plate 26, an upper thermal plate 27, an upper die 28,an intermediate die 29, a lower die 31, another thermal insulating plate32 and a lower platen 33 are placed in this order. A parting face 34between the upper die 28 and the intermediate die 29 is sealed by anO-ring (sealing means) 35 fitted in a fitting groove 29 a on the upperface of the intermediate die 29. A parting face 36 between theintermediate die 29 and the lower die 30 is sealed by another O-ring 37fitted in a groove 30 a on the surface of the lower die 30. A closedspace 38 closed by the O-ring 35 and 37 is in vacuum by the vacuum pump24. There is a cavity 39 on the surface of the lower die 30. In thecavity 39 a porous carbon plate (sheet) 40 is set. The upper surface ofthe plate 40 has a groove (cutted groove) 40 a or concave portion intowhich liquid rubber (molding composition) flows via a spool 41, a runner42 and a gate 43, thereby a gasket is molded. The gasket is unitizedwith the porous carbon plate 40 when molded. Example of the plate is acurrent-collecting electrode (separator) 2 of the fuel cells, anion-exchange membrane 3 interposed between the current-collectingelectrode 2 or a reaction electrode 4 which is fixed to the ion-exchangemembranes or the like. The porous carbon plate is made of carbon orgraphite. The groove 40 a is formed for preventing displacement of thegasket from its initial place in use. If there is no displacement of thegasket in use there is no need to form the groove.

[0128]FIG. 3 shows a control diagram. In die closing process, dieclosing operation is once stopped at a predetermined position (S 101 inFIG. 3) before final die closing operation. During this die stoppingoperation, dies are left at a predetermined position from each otherusing a die holding means. This predetermined position is set to makecontact the O-ring 35 and 37 with each of the upper and lower die, andis set to make the length of the interspace between the parting face 34and 36 into not more than 2 mm. This predetermined position does not letenvironmental air flow into the closed space 38 during vacuum operation.Then the nozzle 22 makes ahead toward the mold to touch the upper mold28 (S 102 in FIG. 3). The contact strength of the nozzle 22 to the uppermold 28 is set in a range not to cause air leakage from the environment,generally is set not less than 2 KN. Thereby the closed space 39 is shutcompletely from the environment except the the passage which isconnected to the vacuum pump 24.

[0129] The vacuum pump 24 starts to operate after the contact strengthof the nozzle 22 to the upper mold and a limit switch operates or aftera predetermined time from the making ahead operation of the nozzle 22 (S103 in FIG. 3). During the vacuum operation, the shut-off valve 23(closing means) in the nozzle 22 is shut so as not to let the moldingcompound flow into the mold.

[0130] After a predetermined period of time (for example not less thanabout 15 seconds) from the beginning of the vacuum operation or apredetermined vacuum pressure (for example not more than about 10 Torr)is attained, further-die-closing operation is carried out (S 104). Thepressure of the further-die-closing operation is not more than thepressure the porous carbon plate 40 is damaged even if the moldingcompound is injected into the mold. The pressure should also be set tothe pressure not more than that of the molding compound flowing out ofthe mold to make burr. It is desirable that the pressure is set not morethan about 100 MPa when a porous carbon plate 40 having thickness of 2mm made of resin-immersed type carbon plate (IKC-33, by Toyo Carbon Co.)is used. The dimensions of the width and the depth of the groove are 3.0mm and 0.3 mm respectively.

[0131] The molding composition can preferably be selected from siliconetype liquid rubber or perfluoro type liquid rubber. Experiment wascarried out using silicone type liquid rubber (KE1950-20(A.B)) havingviscosity of 150 Pa·s (at 25° C.) and having a hardness of 20 (JIS A)after curing. Injection molding was carried out at about roomtemperature so as not to cause curing reaction (for example at thetemperature not more than 20° C.). Temperature of the mold was set atwithin the range of about 120° C. to 180° C., preferably at 150° C. Thepressure of the injection molding is preferably within the range ofabout 2 to 30 Mpa, more preferably of about 20 MPa. The pressure of theinjection molding of the Embodiment was carried out at 20 MPa. Andcuring time was 150 seconds.

[0132] The thus obtained gasket is formed on a groove 40 a of thesurface of a plain porous sheet 40 such as a current-collectingelectrode 2 or an ion-exchange membrane 3 or a reaction electrode 4combined with the ion-exchange membranes. The objects of the presentinvention can be achieved by the gasket having thin in thickness, anexcellent processability in assembling fuel cells, difficulty indisplacement, an excellent sealability at low sealing pressure anduniform sealing pressure all around the gasket. The thus obtained gasketalso has merits such as decreasing the number of parts, preventingdisplacement of gasket in long use under pressure, stabilizing thedimensions of the parts, decreasing problems in assembling fuel cells,decreasing instability and inefficiency in the operation of fuel cellsdue to inadvertent lack of parts in assembling, decreasing molding flaw,stability of processability in molding, improving in sealing ability,simplifying in mold structure, decreasing in step of molding, decreasingin step of adhesion, decreasing in cost, decreasing in cycle time,decreasing in leakage by burr or the like.

[0133] Embodiment 11

[0134]FIG. 4 shows another embodiment of the present invention. In theporous plain sheet 40, two grooves 40 a and 40 b are made on both sideof the sheet respectively. As is shown in FIG. 5, grooves 40 a and 40 bis connected by a plurality of hole 40 c at bottoms of the grooves. Thediameter of the hole is about 1 mm. These holes is formed along thegasket at a intervals of about 10 to 20 mm.

[0135] As is shown in FIG. 6, when molding composition flows onto thesheet, two gaskets 7 and 8 are molded into two grooves 40 a and 40 bsimultaneously via holes 40 c in one body. This type of gasket also hasmerits such as thin in thickness, improving in assembling process,preventing displacement in use, an excellent sealability at low sealingpressure, uniform sealability all around the gasket. This type of gasketalso has merits such as decreasing the number of parts, preventingdisplacement of gasket in long use under pressure, stabilizing thedimension of the parts, decreasing problems in assembling fuel cells,decreasing instability and inefficiency in the operation of fuel cellsdue to inadvertent lack of parts in assembling, decreasing molding flaw,stability of processability in molding, improving in sealing ability,simplifying in mold structure, decreasing in step of molding, decreasingin step of adhesion, decreasing in cost, decreasing in cycle time,decreasing in leakage by burr or the like.

[0136] The gasket 7 and 8 have foot portions 7 a and 8 a which are ingrooves 40 a and 40 b, and seal portion or lip or mountainous portion 7b and 8 b. These two gaskets are made in one body via rubbervulcanizates 9 formed in the holes 40 c.

[0137] In this embodiment the foot portion 40 a and 40 b can beeliminated. If there is no foot portion, the holes 40 c opens directlyon both surfaces.

What is claimed is:
 1. A gasket for layer-built fuel cells, the gasketbeing formed in one body at least on one of a surface of a sheet, thegasket being comprised of a vulcanizate of a composition comprising aliquid rubber selected from a group consisting of a liquid perfluororubber, liquid silicone rubber, a liquid nitrile rubber, a liquidethylene-propylene-diene rubber and a liquid fluoro rubber; wherein thesheet is selected from a group consisting of a porous carbon sheet madeof a carbon powder, a porous carbon sheet made of a carbon fiber and anion-exchange membrane.
 2. The gasket for layer-built fuel cellsaccording to claim 1, wherein the liquid rubber having a viscosity ofnot more than about 10⁴ Pa·s at 25° C.
 3. The gasket for layer-builtfuel cells according to claim 2, wherein the vulcanizate has a hardness(JIS A) of not more than about
 60. 4. The gasket for layer-built fuelcells according to claim 2, wherein the vulcanizate have a hardness (JISA) of within the range of about 40 to
 5. 5. The gasket for a layer-builtfuel cells according to claim 2, wherein the composition comprises aperfluoro rubber having a viscosity of not more than about 10⁴ Pa·s at25° C. and a polytetrafluoroethylene fine powder.
 6. A method for makingthe gasket on the sheet according to claim 1, the method comprisingfollowing steps of; preparing at least two molds having a groove bywhich the gasket is formed, wherein the mold has a sealing means arounda peripheral portion thereof, a passage through which air can flow outof the mold and an inlet on one of the mold through which the liquidrubber can flow into the groove, placing the sheet between the two moldsand closing the molds so as the sealing means on one of the mold tocontact on a surface of the other mold, closing the inlet by a closingmeans stalled in a tip of an injection nozzle so as to make a closedspace closed by the O-ring and by the tip, sucking air out from theclosed space until a degree of vacuum reaches to a predetermined value,and injecting the liquid rubber into the mold; the injection moldingbeing carried out under at an injection pressure within a range of about2 to about 30 MPa.
 7. The method for making the gasket on the sheetaccording to claim 6, wherein the predetermined value is not more than20 Torr.
 8. The method for making the gasket on the sheet according toclaim 6, wherein the predetermined is not more than 10 Torr.
 9. Themethod for making the gasket on the sheet according to claim 6, whereinthe injection pressure is in the range of about 2 to 20 MPa.